Plugin creation

You’ve built a few rules now, and you think you’ve wrote something that’s useful in a more general sense. So, rather than copy & paste between all your Dangerfiles, it’s time to move that code into a plugin.

A plugin in this context is nothing too special, it’s a Swift Package Manager library that you create which exposes some functions to your Dangerfile. With luck, you should be able to basically copy and paste your rules - add a test or two and then you’re good to go.

You can get started by making a new SwiftPM package, chance are you’ve never done this, so lets run through it here:

Start by making a new folder, then making a new package:

mkdir DangerNoCopyrights/
cd DangerNoCopyrights/
swift package init --type library

  Creating library package: DangerNoCopyrights
  Creating Package.swift
  Creating .gitignore
  Creating Sources/
  Creating Sources/DangerNoCopyrights/DangerNoCopyrights.swift
  Creating Tests/
  Creating Tests/LinuxMain.swift
  Creating Tests/DangerNoCopyrightsTests/
  Creating Tests/DangerNoCopyrightsTests/DangerNoCopyrightsTests.swift
  Creating Tests/DangerNoCopyrightsTests/XCTestManifests.swift

You will need to add Danger as a dependency, if you want to work with Xcode, first run swift package generate-xcodeproj to create an Xcode Project, then edit your Package.swift:

    dependencies: [
        // Dependencies declare other packages that this package depends on.
-       // .package(url: /* package url */, from: "1.0.0"),
+       .package(url: "", from: "0.7.3")
    targets: [
        // Targets are the basic building blocks of a package. A target can define a module or a test suite.
        // Targets can depend on other targets in this package, and on products in packages which this package depends on.
            name: "DangerNoCopyrights",
-           dependencies: []),
+           dependencies: ["Danger"]),
            name: "DangerNoCopyrightsTests",
            dependencies: ["DangerNoCopyrights"]),

Make those changes and run swift package update to have Swift PM add Danger to your dependencies. For writing something simple, you can expose a single function in your library:

import Danger
import Foundation

public func checkForCopyrightHeaders() -> Void {
    let danger = Danger()

    let swiftFilesWithCopyright = danger.git.createdFiles.filter {
        $0.fileType == .swift
            && danger.utils.readFile($0).contains("//  Created by")

    if swiftFilesWithCopyright.count > 0 {
        let files = swiftFilesWithCopyright.joined(separator: ", ")
        warn("Please don't include copyright headers, found them in: \(files)")

#Writing your Plugin

If you write a plugin you can import danger directly on the Package.swift, this will make easier to test the plugin

let package = Package(
    products: [
        .library(name: "DangerPlugin", targets: ["DangerPlugin"]),
        .library(name: "DangerDeps", type: .dynamic, targets: ["DangerPlugin"]), // dev
    dependencies: [
        .package(url: "", from: "1.0.0"),
    targets: [
        .target(name: "DangerPlugin", dependencies: ["Danger"]),

(Recommended) Use Rocket, or a similar tool, to comment out the DangerDeps library from the Package.swift. This prevents the DangerDeps library compiled with your plugin by users.

#Adding it to your Dangerfile

You can find all the informations about how to add plugins to a Dangerfile at Plugins

#Part Two

This is enough to get started, if you want to move it up a level check out Extending Danger Two.

Got improvements? Help improve this document via sending PRs.